The technical field generally relates to aftertreatment systems for internal combustion engines. The introduction of aftertreatment systems into the exhaust systems of internal combustion engines also introduces a number of related challenges and drawbacks.
In one example, a NOx reduction system provides a capability to reduce NOx emissions from the engine. However, it is desirable to detect whether the NOx reduction system is properly or sufficiently reducing NOx gases. One method to determine whether the NOx reduction system is operating properly is to put a NOx sensor downstream of the NOx reduction system. However, in certain engine operating conditions, the system will be operating properly, yet the engine will be producing enough NOx that the NOx sensor detects NOx output and the system may appear to be in a failed condition. At certain engine operating conditions, the engine may be producing a small amount of NOx such that even a failed NOx reduction system is capable of converting virtually all of the presented NOx and the system may appear to be operating properly.
Certain systems for aftertreatment rely upon an active component (e.g. a selective reduction catalyst (SCR) component), upon a reagent (e.g. urea to provide NH3 to the SCR component), and/or upon a reagent delivery system (e.g. a reagent injector). Certain failures of these systems produce failures that are difficult to detect, and/or difficult to identify a source of the failure. For example, it is challenging to distinguish between a failed catalyst on the SCR component, a failed reagent (e.g. a urea reagent container erroneously or improperly filled with water), and a failed reagent delivery system.
Certain systems for aftertreatment rely upon having both upstream and downstream NOx measurement of the reduction catalyst to determine if the catalyst NOx conversion has degraded. Certain systems for aftertreatment rely upon inlet NOx determinations and reductant injection rate determinations that have high accuracy and precision to determine if the catalyst NOx conversion efficiency has degraded.
Therefore, further technological developments are desirable in this area.